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Post by madpatty on Jul 19, 2014 10:39:00 GMT -5
And More, Cheers, Patty
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Post by madpatty on Jul 19, 2014 10:43:20 GMT -5
Not much work left now... Fuel manifold, hole placement and evap tubes only left....
If anyone can share any information regarding hole placement and evap tubes etc.
Cheers, Patty
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Post by finiteparts on Jul 19, 2014 10:51:01 GMT -5
Hi Patty, I think it might be worth trying to put the vaporizers into the model and then rerunning the CFD to see how the flow down the vaporizers change things. While I think that you shouldn't get too hung-up on the numbers, your CFD should be able to steer you in the right direction as to the placement and hole sizing, vaporizer locations, etc...The real beauty is that you can run multiple models before you build and hopefully give yourself the best option. Early combustor development was done on water flow tables...the combustor model would be built from clear plastic and the water would be seeded with dye or oxide particles that they could track with cameras. There are several papers from the 1960's from Rolls Royce(in "Combustion in Advanced Gas Turbine Systems", I.E.Smith, Pergamon Press (book)), where they discuss the development of the RB162 combustor and the Spey combustor in which they did the majority of the flow visualization (cold flow only, obviously) with a water table. I have a few Spey combustors and here is a photo of one... The features that you are looking for in a combustor is a region to stabilize the flame, vigorous mixing regions and proper dilution jet penetration. The region of flame stabilization is usually a swirling flow, because the center of the swirling flow has a very low static pressure and acts as a stable anchor to the flame, into which the rest of the swirling flow keeps bringing in a new mixer of unreacted air and fuel. The swirling flow also produces a vigorous shearing action, which helps to mix up the air and fuel so that the reaction zone is fed with a very even mixture. The shear can also help to break up large liquid fuel droplets into smaller, faster vaporizing and burning droplets. After the primary zone, you want to have a lower amount of turbulence so that the reaction has time to complete. You may also have to bring in some more air to help the reaction continue, but if you have a cold air jet that is too big or a really turbulent region, you can extinguish the reaction (flame front), due to too much flame stretching or by what is termed "freezing" the reaction, where the heat from the reaction is dissipated to the cold jet coming in to a point where there is not sufficient thermal energy to keep the chemical reaction progressing...thus incomplete combustion and tons of carbon monoxide out the exhaust. Finally, the dilution jets are included to bring the bulk gas flow temperature down to a level that is acceptable to the turbine. So if the diluton jets don't penetrate deep enough, you can get a hot streak of gas persisting into the turbine. This is less of a concern on radial turbines due to the longer mixing time after the combustor exit plane, but if you can get a more even "mix" of gas in your combustor design, why wouldn't you? So the key takeaway is that although the actual flow speeds and directions may be slightly different in the fired case, cold flow design is a very useful tool that can get you in the ball park. I look forward to seeing more if you get the chance to do it. Thanks for sharing! ~ Chris
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Post by finiteparts on Jul 19, 2014 11:53:07 GMT -5
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Post by madpatty on Jul 19, 2014 12:44:03 GMT -5
Thanks Chris, Very informational....
Those pics in the last of the post will surely be very helpful in designing a homemade combustor...
Those swirl ports in the primary zone i am surely going to follow in my design...
Cheers, Patty
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Post by Johansson on Jul 19, 2014 17:22:35 GMT -5
Please donĀ“t take this the wrong way Patty, you are doing an awesome job of designing and building your engine in record time. It is only that every time I check in on this thread and read about your questions and progress I picture a guy running flat out down a steep hill with no way of braking at all, he just speed on hoping to keep up the pace until the track starts to even out. Keep up running at full speed Patty, I enjoy every second of your build and I really hope you end up with an engine that runs in the end. I had somewhat of a giggle when you posted the pictures above and followed up with the statement that it was not much left to do, when my engine looked like that I spent another year and a half working on it before it ran. /Anders
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Post by madpatty on Jul 19, 2014 21:03:01 GMT -5
Thanks Anders....
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Post by madpatty on Jul 19, 2014 21:28:20 GMT -5
Hi Racket,
In my case the difference in the length "Axially" between the inner and outer flametube is about 40mm... Inner wall of flametube is 50mm and outer wall of flametube is 90mm....
In that case how to place the holes axially, Especially the Tertiary ones....? Because i always thought that holes at each region should be at same axial distance....
Moreover,you shared ROT's somewhere in which you've mentioned that Total flow area of Evap's should be 10% of the total hole/inducer area.... Total flow area is "inner cross sectional area multiplied by number of tubes"??
Thanks, Patty
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Post by racket on Jul 19, 2014 22:41:32 GMT -5
Hi Patty
Total evaporator cross sectional flow area should amount to ~10% of the flametubes total hole area , and the flametubes total hole area is equal to the compressor wheels inducer area.
If your inner flametube wall is shorter than the outer wall by a large amount as in your case , then place the Tertiary holes in the outer wall only , as long as the Tertiary dilution air gets into the flametube flow and has time to mix and dilute the flow temperature before getting to the NGV , she'll be right .
There are differences between single can flametubes and annular flametubes , we simply accommodate those differences.
Cheers John
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Post by madpatty on Jul 21, 2014 11:16:40 GMT -5
Hi Racket,
I have welded 12 tubes with 5mm ID and 8mm OD as my evap tubes.... They are according to the area calculations but visibly bore appears a bit less....hopefully there's nothing like "Minimum ID"??
Thanks, Patty
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Post by madpatty on Jul 21, 2014 11:36:52 GMT -5
Moreover if anybody can suggest the methods of how i can squirt the fuel into the EVAP tubes... I am looking forward to use syringe needles with 0.8 mm OD for diesel...but the problem is how to weld them to the fuel manifold...
Is soldering of any good?? It melts at relatively low tempeatures so i am sceptical if it can withstand the heat inside the engine close to NGV...
Thanks, Patty
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Post by racket on Jul 21, 2014 16:47:00 GMT -5
Hi Patty
I use high silver content silver solder to fix my syringe needles into the fuel manifold.
Cheers John
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ashpowers
Veteran Member
Joined: February 2011
Posts: 207
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Post by ashpowers on Jul 22, 2014 9:39:36 GMT -5
Hmmmm. I've never looked at the T62's combustor before but that is very useful info for my reverse-flow TV94 turboshaft engine I'll be getting back onto in the very near future. I was going to use j-tube evaporators like in the T04 engine but I do like how that layout produces a double recirculating zone at the head of the combustor as well as sheet cooling of the walls at the same time.
I use SafetySilv for brazing my fuel manifold parts - and with the black flux. Works very well and you can use a propane torch to braze it. Although I would probably recommend welding the evap tubes to the liner walls though since they will be more likely to experience high enough temperatures to melt silver-bearing braze material.
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Post by madpatty on Jul 22, 2014 9:52:20 GMT -5
Hi Ashpowers, A didn understand when u said
"Although I would probably recommend welding the evap tubes to the liner walls though since they will be more likely to experience high enough temperatures to melt silver-bearing braze material."
In my case i have welded evap tubes to the plate already welded to NGV's... Fuel manifold is kind of floating arrangement between outer casing and NGV plate with minor clamping to secure it at place....
Is there any way other than brazing etc. to secure needles to the fuel manifold?? Because all those high melting point alloys for brazing are not available here...
Cheers, Patty
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Post by madpatty on Jul 22, 2014 14:01:04 GMT -5
Hi Racket, Can you suggest any other ways of how to get fuel inside the evap tubes???...i am facing difficulty in arranging the required solder...i am doubtful with the current soldering if it can survive the heat...
thanks, Patty
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